It is common practice to hold a workpiece with locking pliers while grinding edges or other parts of the workpiece with a grinding machine. Likewise, it is common practice when drilling a small workpiece to hold the workpiece in a desired position with locking pliers in one hand while manipulating a machine such as a drill press with the other hand.
In either situation, the pliers will lose grip on the workpiece if the machine in question imposes a torque or twisting force sufficient to overcome the gripping force of the pliers. The problem can be exacerbated if the gripping force is not uniformly distributed over the surface area of the grip. While the gripping force applied by locking pliers may be substantial, the hold or resistance offered by the grip will be weakened if it is concentrated to a point contact with the workpiece. This problem may accrue because either the workpiece or the pliers or both, have irregularly machined working surfaces. For the workman, the result is often a frustrating loss of grip which impedes the work at hand and which can lead to damage to the workpiece.
Accordingly, there is a need for a new and improved apparatus to portably hold workpieces during drilling, grinding or similar operations.
The prior art is replete with designs for locking pliers or clamps. This includes locking pliers that have been marketed and sold for years under the trademark VISE-GRIP design variations thereof; see also U.S. Pat. No. 2,563,267 (Petersen) granted on Aug. 7, 1951. Other examples include those disclosed in the following U.S. patents: U.S. Pat. No. 5,385,072 (Neff) granted on Jan. 31, 1985; U.S. Pat. No. 4,730,524 (Petersen) granted on Mar. 15, 1988; U.S. Pat. No. 5,460,065 (Balmer) granted on Oct. 24, 1995; U.S. Pat. No. 5,765,822 (Mead) granted on Jun. 16, 1998; U.S. Pat. No. 5,992,273 (Galea) granted on Nov. 30, 1999; U.S. Pat. No. 6,000,686 (Yates) granted on Dec. 14, 1999; U.S. Pat. No. 6,012,361 (Wooster et al.) granted on Jan. 11, 2000.
The prior art is sparse with examples of designs which advocate the use of a pair of locking pliers or clamps. Those of which the applicant is aware are directed to situations where one of the pair of pliers or clamps is used to hold a workpiece while the other is used for connection with a supporting structure such as a table, thereby allowing the workpiece to be held in a desired angular position relative to the table: see U.S. Pat. No. 1,352,647 (Benton) granted on Sep. 14, 1920 and U.S. Pat. No. 5,058,869 (Ruthven) granted on Oct. 22, 1991. None of these examples address or contemplate the situation where a workman uses an locking pliers or a clamp to portably hold a workpiece during drilling, grinding or similar operations. Further, they do not address the problem which leads to the undesirable loss of grip on a workpiece during machining operations.
In accordance with a broad aspect of the present invention, there is provided a hand tool is for portably holding a workpiece, the tool comprising first and second locking pliers for concurrently gripping the workpiece with a lockable grip, and a bracing member for restraining relative movement between the pliers while both of the pliers concurrently grip the workpiece. Each of the pliers comprises a first elongated handle member having a fixed jaw member at one end and opposed sides; a movable jaw member pivotally connected to the first handle member for movement on a pivot axis between an open position and a closed position in relation to the fixed jaw member; a second handle member pivotally connected to the movable jaw member for moving the movable jaw member between its open and closed positions; and a locking mechanism for releasably locking the movable jaw member in its closed position. The bracing member extends from the first handle member of one of the pliers. When the pliers concurrently grip the workpiece, the bracing member serves to restrain relative movement between the pliers by engaging an abutment carried by the first handle member of the other one of the pliers.
With the use of first and second locking pliers and a bracing member therebetween, an improved grip on a workpiece can be achieved. In other words, the torque required to twist a workpiece from the grip of the two pliers when they are braced in accordance with the present invention is greater (and can be substantially greater) than the torque required to twist the workpiece from the grip of the two pliers when they are not braced.
In one embodiment, the bracing member comprises an elongated bracing pin which extends on a longitudinal axis transversely from the first handle member of one of the pliers, and a pin abutment fixed to the first handle member of the other one of the pliers to provide an abutment for the bracing pin. The pin abutment may comprise a socket sized to longitudinally receive the bracing pin. In a preferred embodiment, the bracing pin is connected to and is preferably integrally formed with the jaw pivot pin of a first one of the pliers, and the pin socket is connected to and is preferably integrally formed with the jaw pivot pin of the other one of the pliers.
Advantageously, the pin socket is sized not only to longitudinally receive the bracing pin but also to permit angular movement of the bracing pin within the socket in a plane perpendicular to the longitudinal axis of the bracing pin. This allows the socket to provide an abutment for the bracing pin while the pliers are angled towards each other for the purpose of concurrently gripping a relatively small workpiece.
In another embodiment, there is provided a hand tool for portably holding a workpiece, the tool comprising first and second locking pliers having substantially the same construction including a first pin socket connected to the first handle member of a first one of the pliers; a second pin socket connected the first handle member of a second one of the pliers: and an elongated bracing pin extending on a longitudinal axis. One end of the bracing pin is longitudinally receivable within the first pin socket while an opposed end of the bracing pin is longitudinally received within the second pin socket. The pin sockets are for concurrently abuttingly engaging the bracing pin while both of the pliers concurrently grip the workpiece. This embodiment enables the use of first and second locking pliers that are substantially the same in construction. Further, as will become apparent hereinafter, this embodiment may incorporate added features like those described above.
The foregoing and other features and advantages of the present invention will now be described in more detail with reference to the drawing.